Background: Sodium-glucose cotransporter-2 inhibitors (SGLT-2i's) improve heart failure (HF) related outcomes. The mechanisms underlying these benefits are not well understood, but diuretic properties may contribute. Traditional diuretics, such as furosemide, induce substantial neurohormonal activation contributing to the limited improvement in intravascular volume often seen with these agents. However, the proximal tubular site of action of the SGLT-2i's may help circumvent these limitations. Methods: 20 patients with type-2 diabetes and chronic, stable HF completed a randomized placebo-controlled crossover study of empagliflozin 10mg daily vs. placebo. Patients underwent an intensive 6-hour biospecimen collection and cardio-renal phenotyping at baseline and again after 14 days of study drug. After a 2-week washout, patients crossed over to the alternate therapy with repeat of the above protocol. Results: Oral empagliflozin was rapidly absorbed as evidenced by a 27-fold increase in urinary glucose excretion by 3 hours (p<0.0001). Fractional excretion of sodium (FENa) increased significantly with empagliflozin monotherapy vs. placebo (FENa 1.2 ± 0.7% vs. 0.7 ± 0.4% p=0.001) and there was a synergistic effect in combination with bumetanide (FENa 5.8 ± 2.5% vs. 3.9 ± 1.9%, p=0.001). At 14 days, the natriuretic effect of empagliflozin persisted, resulting in a reduction in blood volume (-208mL, IQR -536 to 153 mL vs -14mL, IQR -282 to 335 mL, p=0.035), and plasma volume (-138mL, IQR -379 to 154mL ± 453 mL, p=0.04). This natriuresis was not, however, associated with evidence of neurohormonal activation as change in norepinephrine was superior (p = 0.02) and all other neurohormones similar (p<0.34) during the empagliflozin vs. placebo period. Furthermore, there was no evidence of potassium wasting (p=0.20), or renal dysfunction (p>0.11 for all biomarkers), whereas both serum magnesium (p<0.001) and uric acid levels (p=0.008) improved. Conclusions: Empagliflozin causes significant natriuresis, particularly when combined with loop diuretics, resulting in an improvement in blood volume. However, off-target electrolyte wasting, renal dysfunction, and neurohormonal activation were not observed. This favorable diuretic profile may offer significant advantage in the management of volume status in HF patients and may represent a mechanism contributing to the superior long-term HF outcomes observed with these agents. Clinical Trial Registration: URL: https://clinicaltrials.gov Unique Identifier: NCT03029760

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Current pharmacological therapies for heart failure with reduced ejection fraction are largely either repurposed anti‐hypertensives that blunt overactivation of the neurohormonal system or diuretics that decrease congestion. However, they do not address the symptoms of heart failure that result from reductions in cardiac output and reserve. Over the last few decades, numerous attempts have been made to develop and test positive cardiac inotropes that improve cardiac haemodynamics. However, definitive clinical trials have failed to show a survival benefit. As a result, no positive inotrope is currently approved for long‐term use in heart failure. The focus of this state‐of‐the‐art review is to revisit prior clinical trials and to understand the causes for their findings. Using the learnings from those experiences, we propose a framework for future trials of such agents that maximizes their potential for success. This includes enriching the trials with patients who are most likely to derive benefit, using biomarkers and imaging in trial design and execution, evaluating efficacy based on a wider range of intermediate phenotypes, and collecting detailed data on functional status and quality of life. With a rapidly growing population of patients with advanced heart failure, the epidemiologic insignificance of heart transplantation as a therapeutic intervention, and both the cost and morbidity associated with ventricular assist devices, there is an enormous potential for positive inotropic therapies to impact the outcomes that matter most to patients.

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